Secondary battery having improved high-temperature properties

Abstract

A secondary battery comprising a positive electrode current collector, a first positive electrode mixture layer disposed on the positive electrode current collector and including a first positive electrode active material and a binder, and a second positive electrode mixture layer disposed on the first positive electrode mixture layer and including a second positive electrode active material and a binder. A nickel content of the second positive electrode active material is 80% by weight or less of a nickel content of the first positive electrode active material. By providing a secondary battery including a positive electrode of a multi-layer structure that includes positive electrode active materials having different contents of nickel, a secondary battery capable of improving high-temperature characteristics while maintaining energy density may be provided.

What is claimed is: 
     
         1 . A secondary battery comprising:
 a positive electrode comprising:   a positive electrode current collector;   a first positive electrode mixture layer disposed on the positive electrode current collector and including a first positive electrode active material and a binder; and   a second positive electrode mixture layer disposed on the first positive electrode mixture layer and including a second positive electrode active material and a binder,   wherein a nickel content of the second positive electrode active material is 80% by weight or less of a nickel content of the first positive electrode active material.   
     
     
         2 . The secondary battery of  claim 1 , wherein the first positive electrode active material contains 42% by weight or more of nickel. 
     
     
         3 . The secondary battery of  claim 1 , wherein the second positive electrode active material contains 37% by weight or less of nickel. 
     
     
         4 . The secondary battery of  claim 1 , wherein the second positive electrode active material is contained in an amount of 50% by weight or less of the first positive electrode active material and the second positive electrode active material. 
     
     
         5 . The secondary battery of  claim 1 , wherein a thickness of the first positive electrode mixture layer is 30 μm to 100 μm. 
     
     
         6 . The secondary battery of  claim 1 , wherein a thickness of the second positive electrode mixture layer is 1 μm to 50 μm. 
     
     
         7 . The secondary battery of  claim 1 , wherein the first positive electrode active material is at least one selected from LiNi0.7Co0.15Mn0.15O2, LiNi0.8Co0.1Mn0.1O2, LiNi0.9Co0.05Mn0.05O2, and LiNi0.8Co0.15Al0.05O2. 
     
     
         8 . The secondary battery of  claim 1 , wherein the second positive electrode active material is at least one selected from LiNi(⅓)Co(⅓)Mn(⅓)O2, LiNi0.4Co0.3Mn0.3O2, LiNi0.5Co0.2Mn0.3O2, LiNi0.6Co0.2Mn0.2O2, and LiNi0.7Co0.15Mn0.15O2. 
     
     
         9 . The secondary battery of  claim 1 , wherein the binder is at least one selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber (SBR), hydrogenated nitrile butadiene rubber (H-NBR), fluorine rubber, styrene monomer (SM), Butadiene (BD), butyl acrylate (BA), mussel protein, a polyolefin-based binder, and a silane-based binder. 
     
     
         10 . The secondary battery of  claim 1 , wherein the first positive electrode mixture layer and the second positive electrode mixture layer further comprise a conductive material. 
     
     
         11 . The secondary battery of  claim 10 , wherein the conductive material is at least one selected from multi-wall CNT, single-wall CNT or the like; natural graphite, artificial graphite or the like; carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or carbon black of summer black; a carbon fiber, a metal fiber, or the like; a metal powder of carbon fluoride, aluminum and nickel powder, a conductive whisker of zinc oxide and potassium titanate, a conductive metal oxide of titanium oxide, and a polyphenylene derivative.